Experiments are devised to determine the relative importance of early termination of specific arginine-messenger RNAs (arg mRNA) as a control device to modulate regulation of the synthesis of the biosynthetic enzymes made by Escherichia coli for arginine production. We found that during repression with arginine in argR plus cells and in vitro mostly short arg ECBH mRNA (8S) appears, while long arg ECBH mRNA is found concommitant with high levels of argH and argE enzyme synthesis. The short arg mRNA accounts for the excess hybridizable m-RNA found in repressed cells. Our working model is that arginine together with the argR protein and perhaps also the arginyl-tRNA system and other factors modulate transcription by controlling early termination of arg mRNA synthesis. I propose to determine the exact origin and mode of regulation of short vs. long arg ECBH mRNA species, by hybridization against separated strands of lambda darg ECBH DNA following sucrose gradient separation. Using lambda darg DNA's deleted for parts of the ECBH cluster, a tandem hybridization technique is designed to determine and compare control-region RNA with structural gene RNA. Using a series of argR minus strains showing different repression responses, the physiologic affect of arginine upon arg ECBH size distribution and arginine enzyme synthesis will be studied to determine the role of argR on attenuation as well as initiation control. Similar experiments are proposed to determine the role of specific control mutants at the EC boundary and arg S mutants in early termination of argECBH mRNA. Cellular factors affecting specific mRNA size distribution and altering enzyme synthesis will be studied. Using both a purified RNA polymerase, rho system and crude extracts from strains carrying argR minus or arg S, with various lambda dargECBH DNA templates.